AN UNBIASED VIEW OF SWANS EGGS INCUBATION TIME

I am no expert on swans. I rather believe that an evening-time predator filched the eggs. I've listened to individuals express that their birds( chickens, geese, what ever) get rid of infertile or nonviable eggs from their nest. In forty decades I have not experienced a bird clear away their unique egg/s in the nest besides accidentally. How many